We experimentally investigated the effect of density variation on the dynamic behavior of coaxial co-rotating swirling jets, focusing on how the difference of density between the inner and outer jets affect the flow at a high swirl number. When the density of the inner jet is higher than that of the outer jet (ρi/ρo ≈ 1.64. Here, ρi and ρo is the density of the inner and outer jet respectively.), both large-scale vortical structure and stagnating flow is induced by the hydrodynamic shear layer instability become easier to form when compared to that obtained for the case of iso-density jet (ρi/ρo = 1). The velocity field at the inner swirl number, Si = 0.6 is obtained using the Particle Image Velocimetry (PIV) analysis. The velocity field shows the absence of velocity vectors pointing towards the jet core downstream of the CO2 jets stagnation point. In contrast, when the density of the inner jet is lower than that of the outer jet (ρi/ρo ≈ 0.15), the inner jet does not form a stagnating point even at a high inner swirl number (Si = 0.6), and does not significantly change in response to swirl of inner jet.

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